Ever since I started driving my blue VE again these past few weeks (after being down for a year) I've noticed subpar a/c performance in it. It always blew ice cold for me in the past. Nowadays, the system seems to cycle off for long stretches which causes the vent temp to hover at 60 degrees for several minutes at a time. When the compressor does finally engage again the vent temp will work down to low 50's, but only briefly before going right back up to 60.

So basically l get about 3-4 minutes of warmish air (~60 degrees), followed by a very brief period of cool air (30 seconds maybe?), only to be followed again by warmish air, over and over etc.

I put my gauges on it the other day. It was 81 degrees outside at the time and 64% humidity according to the local news.

I put the gauges on with the car off and the low side read 85 PSI and the high side read 90 PSI.

Started the car up and let it idle with the a/c on, compressor immediately engaged, and low side was 32 PSI and high side at 170 PSI. Center vent temp worked down to about 55 degrees and stayed there. Both radiator fans stayed on. The pressure gauges weren't bouncing or anything. Compressor stayed engaged the whole time I was letting it idle (probably 5 minutes or so). After about 5 minutes of constant compressor engagement at idle the pressures were 30 PSI low side and 160 PSI high side.

I then raised the engine speed by manipulating the throttle cable to about 2000 RPM (maybe a little higher - I couldn't tell for sure as I had to guess by the engine sound), low side pressure worked down to about 20 PSI and high side pressure went up to about 220 PSI and then the compressor disengaged. I did this a few times and though the pressures were never identical to 20 PSI low and 220 PSI high, they always seemed to get to about that same range with the engine speed raised before the compressor would disengage.

Pressures at idle with the compressor engaged were always about 30ish low and 170ish high. So the regrigeration "loop" seems fine. Any ideas/input?

 

I'm not going to speculate about the different switches and thermistor which probably aren't the cause. You might just need a recharge and leak test. Neither of which can be done without expensive tools and possibly illegal refrigerant, or retrofit.

 

i would just do a recover, vacuum for 1 hour and then recharge and add dye and go from there. after a year of sitting; it will slowly leak out.

 

Sorry I should have clarified, this one is a '93 so it's R134. My black one is a '92 and still R12, but has a large leak somewhere I need to hunt down, but I have a hoard of R12 still so I'll tackle that one of these days hopefully.

Problem is I don't have a recovery machine (obviously). I guess I'd have to take it to a shop to do that. And the problem with going to a shop for any AC issues they all love to just claim your compressor is bad and that you need the system completely re-done.

It would almost be easier at this point if the system was completely out of refrigerant then I could take it all apart and start fresh with the factory oil level and refrigerant amount and do it all myself. I would just be a ***** and vent it to atmosphere but then I'd lose some oil most likely and wouldn't know how much to add back in.

Do either of you guys have a properly functioning R134 system? Any idea what types of pressures your car sees? I wish now I'd hooked the gauges up previously to get a good baseline.

 

generally...and i stress generally...
what you described seems to be a system that's slightly low on refrigerant.

a honest shop with a decent AC machine will evac the system of what's R134a that's left...then do a vac and check for leaks. then it will do a recharge. if the shop is legit they will just charge you to top it off and wont charge for a full recharge.

if you don't want to spend the $...get a can of R134a and charge like 1/4 to 1/2 a can and call it the day.

 

Well I did end up adding about 3/4 can of refrigerant which did not fix the issue. So after another week of researching it and even starting a thread on an automotive ac-specific forum with no good leads/answers, I decided to break down and have a shop look at it. I had my brother take it to work with him (he's a PepBoys store manager) and had the service tech look at it. Since my brother is the retail store manager I had pretty good confidence they wouldn't blatantly rip me off but I still just don't like having to have a shop do anything on the car. Thankfully my brother was able to make them knock down the "book time" to ACTUAL labor time. Anyway, the tech evacuated and recharged the system and it was still displaying the symptoms I described above. He eventually determined the evap temp sensor was bad (he actually referred to it as a "thermistor" but I've only ever heard of newer Maximas have those). It's about a $90 part from Nissan.

I just got the car back last night and today will be the real test driving it around in the nearly 100 degree heat. We shall see

 

Since you have the R-134a A/C it could be the thermal control amp (that's what Nissan calls it). Before ordering it, check if this TSB applies to you.

http://maxima.theowensfamily.com/tsb/NTB93-123a.pdf

 

Well I'm quite irritated to report that driving it around this afternoon in "only" 95 degree heat, I would describe the a/c as feeling just barely adequate. My back definitely got all sweaty. I forgot my vent temp gauge in my Civic and my brother is driving that car now so I can't do an exact vent temp test. I don't seem to feel the long stretches of warm air like I did previously, but the air still doesn't consistently feel ice cold/crisp like this car used to be, even in nearly 100 degree heat.

Interestingly, Nissan refers to the "thermistor" in that TSB, weird that I couldn't find reference to that term previously with a 3rd gen. The thermistor/sensing bulb is connected to the thermo control amp (ie it's all one piece) correct? Maybe that's why I didn't find reference to it.

How do I determine if my car was built prior to that VIN? Mine was built in May of '93.

 

Yea the thermal amp is one whole piece. You can see the body when you go under the passenger side and the bulb when you take out the frash air vent port.



And checking the VIN from the TSB shows that it was built on Sept of 93.

 

Hmm, okay so my car would definitely fall under that TSB. I actually found your thread from a couple years ago about your switch to all R134a stuff, and you had that picture in your post but they were tiny and wouldn't blow up larger, so thanks for posting this.

Do you know if the thermistor/thermo control amp is replaceable WITHOUT opening the system and removing the evaporator? If so, I'll re-position it myself, as I'm sure the tech knew nothing about the finicky position. The TSB seems to indicate the evaporator does need to be removed, in which case I may be SOL as I don't want to pay for another evac and recharge.

 

What you can do for now is check inside the fresh vent air port and see if the bulb is positioned in the same spot. If not, you can try using long needle nose pliers to reposition it.

I'm not really sure if it's replaceable without splitting the case. It does look like the wire is in between the halves of the case. What you could try is undo the front screws/bolts to see if there's enough clearance to take out the wire/bulb of the amp.

 

How do I check inside the fresh air vent port? I don't see any access to that. I know the blue cable controls the fresh air vent, and when I shine a flashlight at the white center ducting I can see the flap move, but I see no way to see in there.

Do I need to remove the dash or something?

 

You just need to remove the glovebox and then you will see that it's held by screw. Unscrew it and you should be able to move it.

EDIT: If you need to remove the evaporator, then you will need to remove the entire dash.

 

This morning I attempted to remove the lower half of the evaporator box. I was able to remove all the screws around the case except one. There is one screw totally inaccessible between the evaporator box and the firewall. Before I discovered that screw it actually looked like I'd be able to separate the evaporator box without having to remove the evaporator itself or open up the system.

I decided to just cut the lower half of the box open so that I don't have to pay any extra labor at a shop or for another evac/recharge. So I broke out the Dremel and cut it off. You can see the clip was in the super low spot as addressed in the TSB. Here's the original location:



So I moved it up (just about ~2 inches) as per the TSB:



Put the box back together and used a 2 part "plastic weld" at the seam where I cut it open. Went and did some errands today, good mix of city and highway driving and all was well! Amazing a 2" difference in position can make such a difference. Thanks for posting about that, jbbons25. I certainly would have never figured that out on my own.

 

it run now?

 

I guess I should do the same while my car is out of commission.

 

Bump.

Well I put the car on jackstands for a month and a half to finish my turbo build and got it running the other night. Right away I notice the stupid AC doesn't work now. Compressor won't turn on. Light on the dash lights up and the idle speed raises a bit but the compressor and fans don't turn on. I checked the AC fuse under the dash and even replaced the AC relay in the engine bay but still nothing.

I hooked my gauge up to the low side side port and it showed about 100 psi. I can't access the high side port now as my intake charge pipe blocks access. I can only assume the system has good refrigerant. I mean, it was leak tested/evacuated/recharged a month and a half ago. They injected dye at the time and I used my UV light the other night to check for leaks and couldn't find any evidence of a leak, plus the static low side reading seems to imply there is a good charge in it.

I can't imagine why this suddenly isn't working. Only thing different other than the turbo stuff is a Nistune ECU, and I don't see why Nistune would affect the AC. I didn't touch anything on the AC system this past month and a half. I was going to go through the FSM workflow but couldn't find my multimeter.

Anybody know any good checks I can do and/or any ideas? I want to get this sorted out before starting to (try) to tune the car. Pretty frustrating that I specifically put the build on hold to ensure the AC worked properly before installing all the turbo stuff and now this.

 

Okay, well, it's definitely an issue with my Nistune ECU. I swapped in a stock ECU and surprisingly got the car to start with it and the AC works just fine with it. For some reason my Nistune ECU isn't sending power to the AC relay

 

Well that's not what I wanted to hear, I hope I don't have the same issue after buying a bunch of new AC parts. Does anyone here have Nistune with a functioning AC system?
Could you simply bypass the ECU and use a separate relay to activate the AC?

 

I forgot to update this. It's working now. The day after I put my stock ECU in, I stuck my Nistune ECU back in to try to do some tuning since I was waiting to hear back from Matt at Nistune about the A/C. A/C came right on and has worked fine since. Not sure why it wasn't working at first. Go figure.

Beyond that though I am having a heck of a time trying to figure out Nistune. I have my K constant in decent shape I think, because it starts right up, idles fine and drives fine with good AFR's in non-boost driving. I'm still having a hard time grasping exactly how to tune it.

I keep getting a knock sensor code anyway, and the car keeps flipping between the main fuel map and the knock map, even at idle it will sit there and flip flop between the two. That probably explains why I can set my timing perfectly aligned with the pulley mark and the pin, then a few minutes later if I check again the timing mark isn't even close to where it was a few minutes earlier. I need to sort that out first of all, I guess. But not sure what to do really since the KS and harness are both brand new. I'm pretty frustrated with it all at this point. I was (naively) thinking I could get this thing tuned during my three day weekend and be having fun with my new turbo car next week, but at this rate I'd be lucky to understand/tune it all by Thanksgiving